For sure, and the funny thing is that it can be replaced often by replaced by the simpler and more readable
DIR=$(dirname $(readlink -f $0))
However OS X doesn't have readlink, so the longer BASH_SOURCE thing makes sense there.
I started using the longer one, and then I gave up on shell scripting on OS X for other reasons, and didn't go back. So yeah there is a lot of random cargo culting.
In Oil I hope to provide an even simpler method that's built in (and it also has readlink builtin to support this)
So many sysadmins have rudimentary skills and simply copy what works.
I have seen some folks with huge repos of code snippets like that